Ligand-receptor assays, particularly immunoassays, provide sensitive diagnostic tools for the in vitro detection in serum and other body fluids of analytes associated with disease and other physiological conditions of clinical significance.
In the past, immunoassays have typically relied on a polyclonal antibody preparation bound to a solid phase. In such assays, a solution of antigen labeled to permit detection is allowed to compete with antigen in a sample for the solid phase antibody. The extent to which the labeled antigen is bound to the solid phase or is detected in the liquid phase can be used as a measure of the presence and quantity of antigen in the sample being analyzed.
Subsequently, non-competitive immunometric assays became available. In these assays, a polyclonal antibody preparation bound to a solid phase is also used. The sample containing the suspected antigen is allowed to contact the solid phase in order for the antigen to bind to the antibodies on the solid phase. Typically, after an incubation step the sample is separated from the solid phase which is then washed and incubated with a solution of additional polyclonal antibodies which has been labeled, for example with a radionuclide, an enzyme, or a fluorescent moiety, to permit detection.
After this second incubation, the unbound labeled antibody is separated from the solid phase and the amount of labeled antibody in either the liquid phase or bound to the solid phase in an antibody:antigen:antibody sandwich is determined as a measure of the presence and/or concentration of antigen in the sample tested.
More recently, immunoassay processes have been modified to use monoclonal antibodies. For example, U.S. Pat. No. 4,376,110 describes two-site immunometric assays using pairs of monoclonal antibodies, one bound to a solid phase and the other labeled to permit detection. The use of monoclonal antibody pairs which recognize different epitopic sites on an antigen has made it possible to conduct simultaneous immunometric assays in which the antigen and labeled antibody incubations do not require the intermediate steps of prior processes.
In the foregoing immunoassay processes, the solid phase system typically comprises an antibody bound to a bead, or alternatively, an antibody coated on a material such as a membrane or filter, suitable to capture an antigen of interest. At present, the preparation of such solid phase systems characteristically requires activation procedures to facilitate the coating of an antibody to a solid support. Additionally, a backcoating procedure, involving the coating of the solid support with a substance effective to inhibit non-specific binding, is generally required. The activation and backcoating procedures are time-consuming and difficult procedures, and as a result, render the preparation of solid phase systems very costly.
In addition to the above-described limitations associated with the preparation of solid phase systems presently available, it has not been possible to assay a given sample for more than one analyte of interest simultaneously on a single solid phase system. Further, present solid phase systems lack the internal controls (i.e., positive and negative controls) which are essential for a determination of the validity and reliability of an assay. The preparation of solid phase systems for a multiple immunoassay process and/or an internal control system has been, prior to the present invention, very difficult.
Accordingly, there exists a need for a solid phase system which may be prepared more efficiently and which minimizes the difficulty and expense of preparation. Additionally, there exists a need for an improved solid phase system which may be utilized to assay a sample for at least two analytes of interest simultaneously. Further, there exists a need for an improved solid phase system which permits the incorporation of internal controls for the performance of assays.